I am in the process of laying chipboard 8x4 sheet timber on deck joists in the garden prior to laying artificial turf on top to create a patio area.
I have opted for chipboard as marine ply or Fenolick board is too expensive at £82 per sheet.
What can I seal the chipboard with to make it not swell?
The chipboard will be roughly one-one and a half inches away from the soil and that will be covered in plastic sheeting anyway.
I have heard PVA is a good choice?

Chip board is useless outside, even treated it will rot. You could try a resin to seal it but you'll be lucky to get a year out it if its wet. You coul try getting some thick polythene sheet down first, that can be bought in about 8m widths

Yep, waisting a whole lot of time and some cash using chip board.

Chipboard wont last as per above. Dont waste your money and get the proper stuff

Try a different lumber yard?

8x4 sheets of 18mm marine ply at £55 without even trying to shop around for a bulk discount?

http://www.ebay.co.uk/itm/Marine-Ply-Plywood-Plyboard-18mm-BS-10881-2003-/320624246590?pt=UK_BOI_Building_Materials_Supplies_Carpentry_Woodwork_ET& ;hash=item4aa6b1bf3e

Or replace the chipboard every spring?

Bite the bullet and use marine ply, chipboard wont last and you might aswell do it just the once.

http://www.timberclick.com/

£26 a sheet for exterior 18mm ply which will be 100 times better than chipboard. just got to look harder.

Chipboard - outside - turf on top. Forget it. You may be able to liberally coat with something that will last a couple of years, but beyond that it will be mush.

Do the job correctly or not at all. Sorry to be negative but pleased you asked before shelling out and wasting your time.


Ref turfing on top of timber - probs good idea to look at what specialists use as the sub structure before fitting 'living' rooves on buildings.

I get what you are trying to do, but any treatment is likely to affect the resin bond, and any sheets on top of chipboard will not affect damp from below. Some places sell recycled plastic boards these days, might be more durable than timber.

[Edited on 17/7/13 by DarrenW]